The game sometimes fails to boot, and the bookkeeping/high-score reset button has no effect, with a clean board and a rebuilt reset section.

Stern M-200 occasionally will not boot and the MPU reset button does nothing

Cause: The 6800 CPU at U9 has a damaged NMI input (possibly from static through a poorly grounded coin door); the reset button feeds that input.

Checks

• Confirm the reset button and its wiring are good.

Fix

• Replace the 6800 at U9.

Systems

• Stern MPU-200

Games

• Seawitch

Related tips

• Stern games from 1980 on need an M-200 MPU
• Stern M-200 MPU jumper settings by ROM set
• Intermittent MPU faults from old closed-frame chip sockets
• M-200 flashes seven times but the game misbehaves or repeats one number in audits
• Get the MPU booting before you change any ROM jumpers
• A Stern M-200 set for 2732s runs any Bally or Stern game 1977-1985
• Seven flashes but no attract mode
• Testing an MPU in the game with only J4 connected

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)